Plot

Ruby is repairing an old pinball machine in the DOBS den. Just as she finishes, Fenella and Griselda arrive with a way to set a magical alarm in DOBS so that they know when someone shows up. They set the alarm, and Miss Drill sets it off, coming to ask for volunteers to come hiking with her. Everyone buries their faces in their books until she mentions that they can stop off at Cosie's on the way back.

Miss Cackle, hearing about Cosie's, decides she wants to go along, So Miss Drill, Miss Cackle, and the girls head off for the mountatin. Ruby stays behind because she's busy reading about the theory of relativity, and doesn't notice everyone else leave. Ethel then declares official war between The Cauldron Club and DOBS. As Ruby runs for the door, Miss Hardbroom tells her that she's missed the climb already, but congratulates her on reading about the theory of relativity.

Meanwhile, Fenella and Griselda have to research the famous battle of Lucy Fairweather and Harriet Hogweed for their history project. After failing to find any useful information, they wish they could go back in time and view the battle for themselves. When Ruby mentions that it might be possible to do so, she modifies a pinball machine into a time-traveller. They also say something about getting Miss Hardbroom's magic mirror from the staff room (they only teach you that kind of magic in the fourth year).

Harriet Hogweed

To get the girls into trouble, Ethel, Drusilla, Sybil and Clarice swap a wire in the pinball machine. They come back, cast their spells, and... someone claiming to be Lucy Fairweather appears. She says that she left in the middle of the battle with Harriet and Baron Overblow, and that if she doesn't get back, the school will fall down and the descendants of the peasants will disappear.

Fenella and Griselda take this witch to see Miss Hardbroom, while Ruby and Sybil try to undo what Ethel did to the time machine. Unfortunately, another witch appears and claims to be Lucy Fairweather as well. The new Fairweather and the old Fairweather start a battle, and cause general havoc around the school. Miss Hardbroom doesn't know which witch to help.

Just then, Miss Cackle returns, and calls a witches council in the main hall. She sends Mildred and Maud to see how Ruby's getting on with the pinball machine, and sends everyone else to gather the rest of the students.

Mildred and Maud run into the second Fairweather, who says that the two battling witches are equally matched. She then says how terrible it is not to be believed, and Mildred agrees with her. They don't really have time to say much, as the first Fairweather appears and nearly blasts Mildred and Maud in an attempt to hit the second Fairweather.

Mildred and Maud then go to see Ruby, who says that she needs ten more minutes. The first Fairweather appears and apologizes, saying that a good witch can't allow an innocent to be harmed by magic. She disappears again and Maud encourages Mildred to choose which witch is which.

Once everyone is assembled in the great hall, Miss Cackle tells them that they are evacuating the school except for Ruby Cherrytree (who is fixing the time machine), Fenella and Griselda. Mildred and her friends volunteer to stay as well, and they are dispatched to help Ruby carry the pinball machine into the great hall.

Mildred catches up with Miss Hardbroom and says that she has a plan. Miss Hardbroom keeps brushing her off for a while, but then they decide to co-operate. Miss Crotchet, Miss Cackle and Miss Hardbroom call the two Fairweathers to the great hall, and Miss Hardbroom says that she's going to turn Ruby, Fenny and Gris into toads for not less than ten years. Mildred jumps in front of them and tells Miss Hardbroom to stop, and Hardbroom says that she's going to turn Mildred into a tree for the rest of her life.

One of the witches then steps forward to protect the girls, proving that she is a good-hearted witch and therefore the real Lucy Fairweather. Together Lucy and Miss Hardbroom defeat Harriet Hogweed (by turning her into a turtle) and the girls then send Lucy back to her own time, having won her battle.

Quotes

Amelia: “Can't get much loftier than Dragon Peak, Miss Hardbroom, not round here anyway.”Imogen: “Then we have your permission?”Amelia: “Why Not? a good invigorating climb, sounds so refreshing, that I think I'll tag along.”Imogen: You, Miss Cackle? But it’s a hill (realises what she has just said) a ... steep hill.”Amelia: “Yes, Miss Drill, I’m familiar with hills.”Constance: “And Cream Buns.”

HB: "Ruby Cherrytree what have we learned about running in doors?"Ruby: "We've learned that I'm going to miss my climb."